Wet bulb thermometer



Jan. 17, 1950 C. A. MABEY WET BULB THERMOMETER Filed Feb. 1'7, 1945 FIG. I

F|G.5 FIG.6

POROUS SINTERED MATERIAL I N V EN TOR.

CL War of said bulb an annular space sufficient to permit the passage of water by seepage or capillarity. The technique of manufacturing suitable shapes of porous metal articles is well known, one such method being fully set forth in U. S. Letters Patent No. 2,310,061, granted to O. R. Bowen, February 2, 1943. The process disclosed in said Bowen patent involves the mixing of metallic powders in suitable proportions, together with certain substances to act as die lubricants, forming the mixture into an article of the desired shape by briquetting and then sintering the formed article under suitable temperature and atmospheric conditions, for which process no invention is herein claimed.

The open end of the sleeve 13 is terminated by a metallic collar I4, sealed thereto, as by soldering, and also having connected thereto and surrounding the capilliary tube I I an extended tubular portion l formed preferably of material having a relatively low thermal conductivity, such, for example, as stainless steel. The extended portion [5, in turn, is carried by a hollow structure 16, through the wall of which passes in sealed relationship the capilliary tube I I, and

having an attachment opening ll adapted for,

connection to a constant-level water box, not shown in the drawing, or to other suitable source, whereby may be maintained a constant head of water within the sleeve l3.

In assembling the apparatus, the bulb It], being preferably shorter than the sleeve 53, is pushed as far as possible into said sleeve, and the space between the end of the bulb and the collar l4 may be filled with a porous non-conducting medium 18, such as glass wool. In operation, the exterior surface of the sleeve 13 is exposed to the atmosphere whose moisture content is to be determined, and the interior thereof, including such annular space as may exist between the inner walls of the sleeve [3 and the outer surface of the bulb ID, as well as the space occupied by the non-conducting material l8, and the space Within the tubular extension 15, is filled with water supplied thereto through the attachment I1. The water permeates material of the sleeve l3, causing the surface to become moist, and to remain so, whereby the temperature of the assembly, including the bulb in will be the wet bulb temperature required for the purpose of humidity determination. The remoteness of the bulb ID from the mounting I6, and the general non-conducting nature of the interconnection, including the influence of the material [8 within the sleeve E3 in inhibiting convection currents in the contained water, combine to prevent the transfer of appreciable heat between said bulb and said mounting, whereby errors due to undesired heat transfer are reduced to a minimum.

Experiment has shown that the normal surface of sintered metal objects is not readily wetted by water, but that this characteristic is eliminated by natural tarnish. The tendency of a porous sintered metal sleeve in service is therefore to acquire a surface of the desired hydrophilic nature; and it has been found that such a surface, once formed, will be retained, and will remain effective over extended periods of time.

In Figs. 2 and 3 is shown a sleeve 2G formed of porous sintered metal and provided with axially disposed fins 2|, whereby the exposed surface is greatly increased, and the time of response to temperature variations correspondingly reduced. In Fig. 4 is shown an alternative form of sleeve, in which a body part 22 is provided with radially disposed fins 23. The molding processes by which porous metal products are formed readily lend themselves to the manufacture of sleeves having surface conformations such as shown in Figs. 2, 3 and 4; and the relatively great strength of the material permits the use of much thinner sections than would be practicable with a ceramic product.

In Figs. 5 and 6 is shown an alternative form of porous metal sleeve embodying the principle of the invention, and differing from that shown in Fig. 1 primarily in the manner in which the surface is maintained in a moist condition. A temperature-sensitive bulb 25, identical in all respects to the bulb I0 shown in Fig. l, is similarly en.- closed in a sleeve or envelope 26 formed of porous sintered metal. On the upper surface of the sleeve 26 is formed a groove 21, constituting a shallow trough from which water may be distributed over the whole surface of the sleeve. Positioned within the groove 21 is a small tube 28 having minute lateral perforations, whereby, when said tube is connected to a source of water supply at a suitable constant pressure, said water will exude from said perforations at a rate sufiicient to compensate for evaporation, and maintain the surface of the sleeve in a uniformly moist condition. The open end of the sleeve 26 is terminated by a metallic collar 29 sealed thereto and corresponding to collar l4, except that said collar 29 is sealed directly to the capillary tube 311 which extends from bulb 26. It will, of course, be understood that heat-insulating material may be included within sleeve 26, between the bulb 25 and collar 29.

In the construction shown in Figs. 5 and 6, it is not necessary that the water be transmitted through the whole thickness of the porous sleeve 26, which minimizes the possibility of malfunctioning due to the pores in the material becoming clogged with solid matter after long periods of operation. Furthermore, the external application of water eliminates undesirable effect due to possible filling of the pores of the internal surface of the sleeve when reaming the same to its final dimensions, and does away with the need for the extreme care which might otherwise be demanded in this mechanical operation.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

I claim:

1. A wet bulb thermometer comprising a thermometer bulb, a porous metal sleeve covering said bulb at one end and extending beyond the other end of said bulb, and fluid-circulation-inhibiting fibrous material within the portion of said sleeve which extends beyond said other end of said bulb.

2. A wet bulb thermometer comprising a thermometer bulb, a porous metal sleeve covering said bulb at one end and extending beyond the other end of said bulb, fluid-circulation-inhibiting fibrous material within the portion of said sleeve which extends beyond said other end of said bulb, and means for supplying water to the space occupied by said insulating material.

3. A wet bulb thermometer comprising 'a, thermometer bulb, a porous metal sleeve covering said bulb at one end and extending beyond the other end of said bulb, fluid-circulation-inhibiting fibrous material within the portion of said sleeve which elgtends beyond said other end of said bulb, and means for supplying water to said sleeve.

4. A'Wet bulb thermometer comprising a thermometr bulb. having means extending therefrom for connecting said bulb to a temperature-measuring apparatus, a porous metal sleeve surrounding said bulb, said sleeve being of substantially greater length than said bulb and having an open end, fluid-circulation-inhibiting fibrous material in said sleeve between an end of the latter and said bulb, and a fitting secured to said open end and having an opening for passage of said connecting means.

CHARLES A. MABEY.

REFERENCES CITED Thefollowlng references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,122,077 Comfort Dec. 22, 1914 1,481,251 Braemer Jan. 22, 1924 1,484,129 Hermann Feb. 19, 1924 1,586,351 Bristol May 25, 1926 1,632,729 Foote June 14, 1927 1,633,599 Moeller June 28, 1927 10 1,960,802 Backstrom May 29, 1934 2,423,781 Koontz July 8, 1947 OTHER REFERENCES Page 25 of Powder Metallurgy by John Wulif, published 1942 by the American Society for Met- 15 als, Cleveland, Ohio. 

